Random Access Memories are well known in the art and are utilized in applications where a user desires to both Read and Write to the memory. However, in some applications, it is important that the memory be resettable to a predetermined state wherein the logic state of all of the memory cells in the memory is the same. One such application requiring this clearing function is a cache memory. In this type of memory, it is important to have the address tag set to all zeroes upon power up of the system. Typically, this resetting of all memory cells is referred to as "flash clearing" the memory.
Another area requiring clearing of a memory is where security is involved. In these security applications, intermediate memories sometimes are provided in the form of small arrays or a group of registers for storing intermediate data which is protected from outside probing. If for some reason, this portion of the memory were invaded, it would be desirable to have a system whereby the entire contents of the memory could be cleared. However, in such applications, it is important that the memory be cleared in a very short duration of time. This may present a problem since a large number of cells must have the logic states thereof changed from one logic state to the other in this short duration of time. In the worst condition, a large number of the cells will be at the opposite logic state to that of the clear state. This would require a system that can overcome the charge stored by a large number of logic states at one time.
In prior art systems, clearing of the memory cells in an array has been accomplished by sequentially addressing each row of memory cells and then writing a zero thereto. However, this requires an additional onboard counter and a significant amount of time. This would be disadvantageous for a system wherein the memory would necessarily have to be cleared in a very short duration of time, such as security applications described above. There therefore exists a need for a memory array having the ability to be cleared to a predetermined logic state within a very short duration of time.